The proposed research is an enzymological and genetic study of the Bacillus subtilis DNA polymerases. We have thus far determined the structural gene for two of the polymerases and have isolated polymerase III mutants which are drug-resistant, conditionally lethal, and mutagenic. The genetics will be extended to mapping of the cistron or cistrons for polymerase III, study of the physiology of polymerase III mutants, characterization of suppressors of the polymerase III defect and, hopefully, isolation of antimutator polymerase III mutants. We plan to isolate physically homogenous preparations of polymerase II and III and to characterize them. We will use purified preparations of wild-type, mutator, and, if available, antimutator polymerase III to explore the fidelity of replication. A major goal is to elucidate at the molecular level the mechanism of inhibition of polymerase III by arylazopyrimidines which are potent antimicrobials. We will examine the kinetics and template specificity of inhibition as well as the effects of chemical modification of the drugs. Physical techniques including x-ray crystallography will be used to detail the novel basepairs formed by the drugs.